This PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life will help you in revision during exams.
PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life
→ All living organisms around us are complex structural compartments called cells.
→ A.V. Leeuwenhoek (1674) first studied the living cell. He examined bacteria, sperms, and erythrocytes (RBC).
→ The biosphere is the highest level of organisation of living organisms.
→ Level of organisation is Atoms → Elements → Cell → Tissue → Organ → Organ System → Living Organisms.
→ Robert Hooke (1665) examined dead cells,
→ Rober Brown (1831) observed the nucleus in the centre of cell.
→ Huxley regarded protoplasm as the ‘Physical basis of life’.
→ The cytoplasm is the fluid content of cells present between the nucleus and plasma membrane.
→ It contains metabolites and organelles.
→ Organelles are special components of cells performing specific functions.
→ Cells are of two types i.e. prokaryotic cell and eukaryotic cell.
→ Organisms may be single-celled e.g. Amoeba, CMamydomonas (an algal plant), Paramecium or they are multicellular.
→ Higher plants and animals are made up of a large number of cells.
→ A true nucleus is present, It is generally single-spherical and central in position.
→ The nucleus is separated from the cytoplasm by a double-layered membrane called nuclear membrane. It controls the functioning of cells.
→ The nucleus contains chromosomes composed of DNA and protein.
→ A functional segment of DNA is called a gene.
→ All living organisms start their life cycle from a single cell.
→ Cell size varies from 0.2 – 0.5 micron to 30 micron (one micron = 1/1000 mm ). Nerve cells may be as long as a few metres.
→ A plant cell is bounded by a protective cell wall.
→ A plasma membrane is a living membrane.
→ Mitochondria are rod-shaped, double-membranous, light-microscopic, eukaryotic structures. Inner membranes have cristae and exosomes.
→ Functions: These act as powerhouses or ATP mills as they are sites for cellular respiration and release energy.
→ The centrosome is an animal structure and is formed of two microtubular centrioles, each being formed of 9 triplet microtubules showing a 9 + 0 arrangement.
→ Function: These help in cell division.
→ Basal bodies give rise to cilia or flagella centrioles form.
→ Contractile vacuoles are present in freshwater protozoans.
→ The cell is a Latin word for a little room’.
→ The electron microscope was discovered in 1942.
→ Water obeys the laws of diffusion.
→ The nucleus plays a central role in cellular reproduction, the process by which a cell divides and forms two new cells.
→ Plastids are the largest-sized eukaryotic structures of plant cells. These are of three types: Leucoplasts (colourless and store the food).
→ The primary function of the leucoplast is storage. Chloroplasts (green coloured and are sites of photosynthesis, so-called kitchens of cells)
→ Each chloroplast is a double-membranous structure having grana in its inner chamber.
→ Each granum is formed of many chlorophyll-containing thylakoids present in stacks.
→ Functions: Chloroplasts are sites for photosynthesis.
→ Chromoplasts (coloured and help in pollination of dowers and dispersal of seeds and fruits).
→ The endoplasmic reticulum is an electron-microscopic interconnected network of cisternae, vacuoles, and tubules.
→ It is of two types: RER (cisternae are studded with ribosomes and involved in protein synthesis) and SER (tubules are without ribosomes).
- It is a passageway for intracellular and intercellular transport of materials.
- It gives internal support to the cell.
- SER is involved in the synthesis of lipids and steroids.
- RER is concerned with protein synthesis.
→ Lysosomes are electron-microscopic single membrane-bound vesicular structures of animal cells and contain hydrolytic enzymes.
- These are centres of intracellular digestion and act as both digestive bags and suicidal bags.
- They destroy foreign substances.
- They remove cellular debris.
→ Living organisms are composed of one or a large number of cells. The cell is the structural and functional unit of life.
→ A large number of build-up and breakdown reactions take place in the cell.
→ Life is passed on from one generation to the next generation in the form of cells.
→ Robert Hooke (1665) first discovered cells on the basis of compartments observed in a thin section of the bark of a tree.
→ Prokaryotic cells lack a well-organized nuclear membrane and membrane-bound organelles. They have 70 S type of ribosomes.
→ Eukaryotic cells have a proper nucleus and membrane-bound organelles. 80 S ribosomes are present.
→ The Golgi body is formed of stacked cisternae with swollen ends, vacuoles, and vesicles.
- It is involved in cell secretions such as mucous, enzymes, and hormones.
- It helps in the storage of secretory products.
→ Cell inclusions include reserve food in the form of glycogen granules or lipid droplets or starch grains.
→ Vacuoles and fluid-filled membrane-bound spaces each containing cell sap within a tonoplast, wastes, gases, secretions, etc.
→ Functions: They help in the storage of food, water, and other wastes.
→ Ribosomes are composed of RNA and proteins, granular electron-microscopic particles without membrane.
→ Functions: These act as protein factories.
→ Prokaryotes: The simple organisms called Monerans without a proper nucleus. e.g. Bacteria, Blue-green algae.
→ Eukaryotes: Organisms with true nucleus (plant and animal cells).
→ Organelles: Special living components of cells each performing a definite function.
→ Leucoplasts: Colourless plastids.
→ Centriole: Star-shaped structure present near the nucleus in an animal cell. It forms a spindle during cell division.
→ Genes: They are present on chromosomes and act as carriers of characters from parents to offspring.
→ Lysosome: These are electro-microscopic structures bounded by a single membrane. They are full of digestive enzymes. They are called ‘suicidal bags.’
→ DNA (Deoxyribose nucleic acid): It controls cellular functions and also acts as genetic material.
→ RNA (Ribose nucleic acid): It plays important role in protein synthesis.
→ Cyclosis: Streaming movements of cytoplasm.
→ Autolysis: Self-digestion of the cell by its lysosomal enzymes.
→ Autophagy: Digestion of its own cell organelles or reserve food by the lysosome.
→ Cristae: Infolds of the inner mitochondrial membrane.
→ Chloroplast: Chlorophyll-containing green coloured photosynthetic plastids.
→ Chromoplast: A pigmented plastid.
→ Tonoplast: Vacuolar membrane present around cell sap.
→ Camillo Golgi discovered Golgi bodies and shared Noble Prize in 1906 with Santiago Ramony Cajal for their work on the structure of the nervous system.
→ Nucleoid: A primitive nucleus of prokaryotes, not covered by a nuclear membrane.